If UAC is on now, then Opus should not be elevated.
If UAC is off again, then the @admin code doesn't make much sense. But it's possible it is/was involved in what's happening.
I would like to rule out those two things. Whatever is causing the freeze may be a bug, but we have to work out which detail is triggering it to be able to fix it, if so.
Another thing I just noticed is that @admin is on the same line as the command. The command should be on a separate line:
@admin
"C:\Program Files (x86)\robocopy.exe" "C:\Struct" "{Rs|Please enter the path.\nThen click OK.|Y:\Models\}" /E /ZB /MON:50 /MOT:60 /MIR
If you want to send us a manually generated crash dump made while the freeze is happening, we may be able to look at that and locate the cause.